Note: Descriptions are shown in the official language in which they were submitted.
CA 02556515 2006-08-18
ELECTRO HYDRAULIC ACTUATOR WITH
SPRING ENERGIZED ACCUMULATORS
FIELD OF THE INVENTION
[0001) This invention generally relates to electro-hydraulic actuators, and
more
particularly, to electro-hydraulic actuators having accumulators.
BACKGROUND OF THE INVENTION
[0002] Accumulators are devices that store energy in the form of fluid under
pressure.
Accumulators are useful tools in developing efficient hydraulic systems due to
their ability
to store excess energy and release it when needed. The accumulators can be
used to provide
various functions in hydraulic systems. These functions include leakage
compensation,
pulsation and shock absorption, noise elimination, and load counter-balance.
[0003) Traditional accumulators for electro-hydraulic actuators are the
nitrogen gas
loaded type. These accumulators are generally thought to consist of an elastic
membrane
charged with nitrogen to provide the potential energy to the hydraulic fluid
to operate the
actuators. The elastic membranes deteriorate over time, resulting in the
nitrogen leaking
into the hydraulic fluid. Typically, the nitrogen escapes slowly as the
membrane
deteriorates over time with no way of detecting the leak. The unknown failure
of the
accumulator can lead to unreliable operation of the hydraulic system.
[0004) Additionally, the accumulators are often added as an afterthought in
hydraulic
system designs and are haphazardly mounted around the hydraulic system
wherever there is
room with varying degrees of success.
[0005) The invention provides a failsafe electro-hydraulic actuator that
overcomes the
above-mentioned problems. These and other advantages of the invention, as well
as
additional inventive features, will be apparent from the description of the
invention
provided herein.
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BRIEF SUMMARY OF THE INVENTION
[0006) In one aspect, the invention provides an actuator system having
multiple
accumulators built into the actuator to provide fail-safe functionality. The
integration of the
accumulators results in a fully tested and validated, redundant fail-safe
actuator.
[0007) In another aspect, the invention replaces the membrane and nitrogen
charged
based accumulator with a spring-loaded piston accumulator. With the use of
multiple
accumulators built into the actuator, any accumulator can cease to function
properly when
required and the other accumulators will fully stroke the actuator/valve to
its fail-safe
condition.
[0008) Other aspects, objectives and advantages of the invention will become
more
apparent from the following detailed description when taken in conjunction
with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009) The accompanying drawings incorporated in and forming a part of the
specification illustrate several aspects of the present invention and,
together with the
description, serve to explain the principles of the invention. In the
drawings:
[0010) FIG. I is a schematic view of an exemplary embodiment of a hydraulic
system in
accordance with the teachings of the present invention;
[OOI1) FIG. 2 is an isometric cross-sectional view of the hydraulic system of
claim 1 ;
[0012) FIG. 3 is an isometric partial view of the hydraulic system of claim 1
showing
redundant accumulators;
[0013) FIG. 4 is a cross-sectional view of an accumulator in accordance with
the
teachings of the invention; and
(0014) FIG. 5 is a line diagram of a hydraulic system in accordance with the
teachings
of the invention having the capability of operating as a fail open or a fail
closed system.
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[0015) While the invention will be described in connection with certain
preferred
embodiments, there is no intent to limit it to those embodiments. On the
contrary, the intent
is to cover all alternatives, modifications and equivalents as included within
the spirit and
scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
(0016) The invention overcomes many problems of traditional accumulators by
providing a failsafe electro-hydraulic actuator having multiple accumulators
integrated into
the actuator to provide fail-safe functionality. The integration of the
accumulators results in
a fully tested and validated, redundant fail-safe actuator. The membrane and
nitrogen
charged of the typical accumulator is replaced with a spring-loaded piston
accumulator.
With the use of multiple accumulators built into the actuator, any accumulator
can cease to
function properly and the other accumulators will filly stroke the
actuator/valve to its fail-
safe condition.
[0017) Turning now to the drawings wherein like reference numerals refer to
like
elements, the invention is illustrated as being implemented in a suitable
operating
environment. Although not required, the invention will be described in the
general context
of an electro-hydraulic actuator. Those skilled in the art will appreciate
that the invention
may be practiced with other configurations where accumulators are used.
[0018) Turning now to the figures, a hydraulic actuator I00 is illustrated.
The actuator
I00 is a double acting actuator. Those skilled in the art will appreciate that
the invention
may be implemented on other types of actuators, including, for example, single
acting
actuators. The hydraulic actuator 100 is only one example of a suitable
operating
environment and is not intended to suggest any limitation as to the scope of
use or
functionality of the invention. Neither should the actuator 100 be interpreted
as having any
dependency or requirement relating to any one or combination of components
illustrated in
the exemplary actuator 100.
[0019) The hydraulic manifold 102 provides control fluid to the hydraulic
piston 104
and to accumulators 106. The piston 104 is connected to output rod 108 and may
be used to
control valves (not shown) by connecting the output shaft clevis I 10 to the
valve stem of the
valve. The LVDTs (linear-voltage differential transformer [also known as
linear variable
differential transformer]) 1 I 2 provide position information of the piston to
the electrical
junction box 1 14. While a single LVDT may be used, multiple LVDTs are used
for
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redundancy and increased reliability of the system. Operation of the actuator
is well known
and need not be discussed in detail herein. For purposes of clarity, not all
connections or
piping is shown in the figures.
[0020] Each accumulator 106 is connected to actuator 100 via modular
structures l 16,
I 18. Modular structure I 16 connects an accumulator 106 to the manifold 102
via a
collection block 120. Modular structure 1 I 8 connects the bottoms of the
accumulators to
the actuator 100 and support shafts 122. The modular structures I I6, I I8
have interlocking
flanges with bolt holes for attaching the structures to other structures. The
collection block
120 has passageways to connect fluid in the manifold 102 to the accumulators
106. The
support shafts 122 provide stiffness to the actuator 100. Alternatively, the
modular
structures 116 and 118 along with collection block 120 may be replaced with
hydraulic
tubing that directly connects the accumulators 106 to the hydraulic manifold
102.
[0021 ] The accumulators I 06 replace the nitrogen of typical accumulators
with coil
springs 140. The coil springs 140 are nested within the cylindrical housing
142 and are
seated upon spring seat 144 and the spring bottom plate 146. The spring bottom
plate 146
forms the bottom of the accumulator 106. The nested coil springs 140 and
spring seat 144
are held within cylindrical housing 142 via a spring top plate 148 that is
attached to the
cylindrical housing 142. The accumulators 106 replace the bladder of typical
accumulators
with piston I 50. The piston 150 does not deteriorate over time.
[0022] The piston 150 is located in a sleeve I 52 that, in combination with
the piston
150, forms a storage cavity for hydraulic fluid as will be discussed herein.
The piston 150
has a base 154 that is attached to side wall 156. The side wall 156 is also
connected to
spring seat 144. Seals 158 prevent fluid from leaking into the area of the
accumulator 106
where the springs 140 are located. During operation, the actuator hydraulic
manifold 102
stores energy in the accumulator by allowing hydraulic supply pressure to push
the piston
l 50, thereby compressing the fluid (and the coil springs 140 from their
default state). A
check valve (not shown) prevents sepply pressure from bleeding back into the
supply
system. During normal operation, the compressed fluid remains in the
accumulators 106.
When the valve 100 is required to move to its fail-safe condition (i.e.,
piston 104 is in its
open or closed condition), the manifold releases the stored energy from the
accumulators
106. The compressed springs 140 return to their default state, thereby
releasing and pushing
the compressed fluid (i.e., the stored energy) from the accumulators 106 to
move the
actuator to its safe condition.
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[0023] The use of multiple accumulators 106 provides fault tolerance (i.e.,
redundancy).
If an accumulator fails (e.g., a spring failure, a bound piston, etc.), the
remaining
accumulators provide sufficient energy to move the actuator to its safe
condition. The
charge stored in the accumulators in one embodiment are sized such that the
remaining
accumulators have sufficient stored energy to move the actuator to its fail-
safe condition if
an accumulator fails. In another embodiment, the accumulators are sized to
move the
actuator to its fail-safe condition if multiple accumulators fail.
[0024) It is possible that a spring 140 may fail. In one embodiment, visual
indicators
are provided on the cylindrical housing 142 that allow inspection of the
springs 140 as well
as confirmation of the charge status of the accumulator (i.e., position of
sp~~ng seat 144).
The visual indicators also provide the ability to determine if the piston 1 SO
is bound or
otherwise stuck in the accumulator 106.
[0025] As previously indicated, the accumulators 106 move the actuator to its
fail-safe
condition. The fail-safe condition may be either the open position (i.e., Fail
Open) or the
closed position (i.e., Fail Closed)_ In one embodiment, the actuator is easily
modified in the
field for either Fait Open or Fail Closed by setting the location of plugs 160
-166 located in
the manifold 106. Plugs 160, 162 are installed to put the actuator 100 in a
Fail Closed
mode. Plugs 164, 166 are installed to put the actuator 100 in a Fail Open
mode. The use of
plugs provides the capability of using the same manifold in both Fail Open and
Fail Closed
modes of operation.
[002b] From the foregoing, it can be seen that a high loading actuator with
built-in fail
safes has been described. The invention can be used in many situations. For
example, it
can be used as a steam valve for a steam turbine. Multiple accumulators are
integrated into
the actuator to provide additional reliability. One or more accumulators can
fail and the
remaining accumulators provide sufficient energy to move the actuator to its
fail-safe
condition.
[0027) The use of the terms "a" and "an" and "the' and similar referents in
the context
of describing the invention (especially in the context of the following
claims) is to be
construed to cover both the singular and the plural, unless otherwise
indicated herein or
clearly contradicted by context. The terms ''comprising," ''having,"
"incIuding,~' and
''containing'' are to be construed as open-ended terms (i.e., meaning
"including, but not
limited to,") unless otherwise noted. Recitation of ranges of values herein
are merely
intended to serve as a shorthand method of referring individually to each
separate value
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falling within the range, unless otherwise indicated herein, and each separate
value is
incorporated into the specification as if it were individually recited herein.
All methods
described herein can be performed in any suitable order unless otherwise
indicated herein or
otherwise clearly contradicted by context. The use of any and all examples, or
exemplary
language (e.g., "such as") provided herein, is intended merely to better
illuminate the
invention and does not pose a limitation on the scope of the invention unless
otherwise
claimed. No language in the specification should be construed as indicating
any non-
claimed element as essential to the practice of the invention.
[0028] Preferred embodiments of this invention are described herein, including
the best
mode known to the inventors for carrying out the invention. Variations of
those preferred
embodiments may become apparent to those of ordinary skil l in the art upon
reading the
foregoing description. The inventors expect skilled artisans to employ such
variations as
appropriate, and the inventors intend for the invention to be practiced
otherwise than as
specifically described herein. Accordingly, this invention includes all
modifications and
equivalents of the subject matter recited in the claims appended hereto as
permitted by
applicable law. Moreover, any combination of the above-described elements in
all possible
variations thereof is encompassed by the invention unless otherwise indicated
herein or
otherwise clearly contradicted by context.
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